CHAPTER XXVIII 



ECONOMIC INSECTS 



A little worm in a hickory-nut 



Sang happy as he could be, 

 Oh I live in the heart of the whole round world, 



And it all belongs to me. 



JAMES WHITCOMB RILEY. 



ENORMOUS losses occur from the damage done by insects in 

 the destruction of farm produce and attacks upon livestock, to 

 say nothing of the spread of human disease (Figs. 270 and 271). 

 The loss to farmers alone is estimated at more than one billion 

 dollars annually. To properly combat insects it is necessary to 

 understand their methods of feeding, mode of life, and in many 

 cases a knowledge of their general structure is very helpful. 



True insects have six legs. The body is usually covered with 

 a more or less hard or tough chitinous material. They take 

 their food through mouth parts which are of two different types, 

 either sucking or biting. The method of fighting them depends 

 much upon whether they get their food by biting or by sucking. 



The breathing of insects is through pores or spiracles along 

 the body not through the head. The smothering of certain 

 insects by the use of oils depends upon this structure. 



Insects have good digestive systems and will consume quanti- 

 ties of food very great in proportion to the size of their bodies. 

 This is due to the fact that they use tissues which are easity 

 digested, and because their growth and transformations are some- 

 times quite rapid. 



The power of reproduction among insects is usually so great 

 as to rapidly multiply the species and produce numbers in alarm- 

 ing degrees when their natural enemies are absent. Insects have 

 circulatory systems and have several of the special senses found 

 among higher animals, such as hearing, feeling, smelling, tasting 

 and seeing. Some of these special senses are often very highly 

 developed. 



Metamorphosis. Insects of any kind are usually grouped 



under one of two heads: Those having complete metamorphosis, 



and those having incomplete metamorphosis. Flies, for example, 



have complete metamorphosis ; that is the insect goes through four 



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